High strength composite

ABSTRACT

An article made from at least one network of high strength fibers and a matrix composition that includes a vinyl ester and diallyl phthalate. Preferably, the article is made from at least one prepreg element which includes at least two adjacent layers of the high strength fiber network in the vinyl ester-containing matrix composition. The prepreg element is made by applying a mixture of vinyl ester, diallyl phthalate and a carbon-carbon saturated solvent to the high strength fiber network.

This application is a division of application Ser. No. 08/148,732, filedOct. 29, 1993 pending.

BACKGROUND OF THE INVENTION

The present invention relates to a composite, particularly one that canbe used in ballistic resistant articles, which includes a network ofhigh strength fibers in a vinyl ester matrix material.

Various constructions are known for ballistic resistant composites usedin ballistic resistant articles such as helmets, panels, and vests.These composites display varying degrees of resistance to penetration byhigh speed impact from projectiles such as BB's, bullets, shells,shrapnel, glass fragments and the like. U.S. Pat. Nos. 5,196,252;5,187,023; 5,185,195; 5,175,040; 5,167,876; 5,165,989; 5,124,195;5,112,667; 5,061,545; 5,006,390; 4,953,234; 4,916,000; 4,883,700;4,820,568; 4,748,064; 4,737,402; 4,737,401; 4,681,792; 4,650,710;4,623,574; 4,613,535; 4,584,347; 4,563,392; 4,543,286; 4,501,856;4,457,985; and 4,403,012 and PCT Publication No. WO 91/12136 describeballistic resistant composites which include high strength fibers madefrom materials such as extended chain ultra-high molecular weightpolyethylene.

Typically these fibers are coated, embedded or impregnated in apolymeric matrix material. During production of such composites thematrix materials must be dissolved in a solvent so that they are in aliquid form for application to the high strength fibers. The solventthen must be removed, usually by drying, in order to fabricate thecomposite.

Of particular interest among the above disclosures is the description ofthe materials that can be used for the matrix material that is found inPCT Publication No. WO 91/12136; column 14, lines 12-36, of U.S. Pat.No. 5,167,876; column 12, lines 25-39 of U.S. Pat. No. 4,820,568; andcolumn 3, lines 1-5 and Example 1 of U.S. Pat. No. 5,165,989. Thesedisclosures describe the use of a vinyl ester as the matrix material.This vinyl ester matrix material is the condensation product of epoxideresins and unsaturated acids that is diluted in a compound having doublebond unsaturation such as a vinyl aromatic monomer as for examplestyrene, vinyl toluene and diallyl phthalate. A problem with these vinylester matrix materials is that the required unsaturated solvents have ahigh boiling point, thus necessitating more energy and time for removalof the solvent. A further problem with many of the organic solvents isthat they require strict handling and disposal procedures because ofpotential environmental or health hazards.

A need exists, therefore, for vinyl ester matrix materials which do notrequire such troublesome solvents, but which provide adequate levels ofballistic performance, mechanical performance and chemical resistance.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide acomposite which includes a matrix material that utilizes a moreconvenient solvent, but offers a high level of ballistic performance,mechanical performance and chemical resistance. In accomplishing theforegoing object there is provided according to the present invention anarticle comprising at least one network of high strength fibers in amatrix composition, the high strength fibers having a tenacity of atleast about 7 g/d, a tensile modulus of at least about 150 g/d and anenergy-to-break of at least about 8 J/g, wherein the matrix compositioncomprises at least one thermoset vinyl ester and diallyl phthalate. In apreferred embodiment the article is a ballistic resistant article suchas a helmet which includes more than one layer of the high strengthfiber network in the vinyl ester-containing matrix composition.

According to a further embodiment of the invention, there is provided aprepreg element which includes at least two layers of the high strengthfiber network in the vinyl ester-containing matrix composite. Aplurality of such prepreg elements can be molded into a composite.

There also is provided according to the invention a method for producingan article that includes at least one network of high strength fibers ina matrix composition, wherein the high strength fibers have a tenacityof at least about 7 g/d, a tensile modulus of at least about 150 g/d andan energy-to-break of at least about 8 J/g, the method comprisingapplying a mixture of a thermoset vinyl ester, diallyl phthalate and acarbon-carbon saturated solvent and consolidating the coated highstrength fiber network to remove the carbon-carbon saturated solvent.

Further objects, features and advantages of the present invention willbecome apparent from the detailed description of preferred embodimentsthat follows.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described below in more detail with reference tothe drawing, wherein:

FIG. 1 is a schematic representation of a process for making a fibernetwork layer of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an improved composite which isparticularly useful in ballistic resistant "hard" armor articles. By"hard" armor is meant an article, such as a helmet or panels formilitary vehicles, which has sufficient mechanical strength so that itmaintains structural rigidity when subjected to a significant amount ofstress and is capable of being free-standing without collapsing.

As used herein, "fiber" denotes an elongate body, the length dimensionof which is much greater than the transverse dimensions of width andthickness. Accordingly, "fiber" includes monofilament, multifilament,ribbon, strip, staple and other forms of chopped, cut or discontinuousfiber and the like having regular or irregular cross-sections. "Fiber"includes a plurality of any one of the above or a combination of theabove.

The cross-sections of filaments for use in this invention may varywidely. They may be circular, flat or oblong in cross-section. They alsomay be of irregular or regular multi-lobal cross-section having one ormore regular or irregular lobes projecting from the linear orlongitudinal axis of the filament. It is particularly preferred that thefilaments be of substantially circular, flat or oblong cross-section,most preferably the former.

As used herein, "fiber network" denotes a plurality of fibers arrangedinto a predetermined configuration or a plurality of fibers groupedtogether to form a twisted or untwisted yarn, which yarns are arrangedinto a predetermined configuration. The fiber network can have variousconfigurations. For example, the fibers or yarn may be formed as a feltor other nonwoven, knitted or woven into a network, or formed into anetwork by any conventional techniques. According to a particularlypreferred network configuration, the fibers are unidirectionally alignedso that they are substantially parallel to each other along a commonfiber direction.

High strength fibers for use in this invention are those having atenacity equal to or greater than about 7 g/d, a tensile modulus equalto or greater than about 150 g/d and an energy-to-break equal to orgreater than about 8 Joules/gram (J/g). Preferred fibers are thosehaving a tenacity equal to or greater than about 10 g/d, a tensilemodulus equal to or greater than about 200 g/d and an energy-to-breakequal to or greater than about 20 J/g. Particularly preferred fibers arethose having a tenacity equal to or greater than about 16 g/d, a tensilemodulus equal to or greater than about 400 g/d, and an energy-to-breakequal to or greater than about 27 J/g. Amongst these particularlypreferred embodiments, most preferred are those embodiments in which thetenacity of the fibers is equal to or greater than about 22 g/d, thetensile modulus is equal to or greater than about 900 g/d, and theenergy-to-break is equal to or greater than about 27 J/g. In thepractice of this invention, fibers of choice have a tenacity equal to orgreater than about 28 g/d, the tensile modulus is equal to or greaterthan about 1200 g/d and the energy-to-break is equal to or greater thanabout 40 J/g.

Useful high strength fibers include extended chain polyolefin fibers,particularly extended chain polyethylene (ECPE) fibers, aramid fibers,polyvinyl alcohol fibers, polyacrylonitrile, liquid crystal copolyester,glass and carbon fibers.

U.S. Pat. No. 4,457,985 generally discusses such extended chainpolyethylene and polypropylene fibers, and the disclosure of this patentis hereby incorporated by reference to the extent that it is notinconsistent herewith. In the case of polyethylene, suitable fibers arethose of weight average molecular weight of at least 150,000, preferablyat least one million and more preferably between two million and fivemillion. Such extended chain polyethylene fibers may be grown insolution as described in U.S. Pat. No. 4,137,394 to Meihuzen et al., orU.S. Pat. No. 4,356,138 of Kavesh et al., issued Oct. 26, 1982, or afilament spun from a solution to form a gel structure, as described inGerman Off. No. 3,004, 699 and GB No. 2051667, and especially asdescribed in U.S. Pat. No. 4,413,110. As used herein, the term ofpolyethylene shall mean a predominantly linear polyethylene materialthat may contain minor amounts of chain branching or comonomers notexceeding 5 modifying units per 100 main chain carbon atoms, and thatmay also contain admixed therewith not more than about 50 wt % of one ormore polymeric additives such as alkene-1-polymers, in particular lowdensity polyethylene, polypropylene or polybutylene, copolymerscontaining mono-olefins as primary monomers, oxidized polyolefins, graftpolyolefin copolymers and polyoxymethylenes, or low molecular weightadditives such as anti-oxidants, lubricants, ultra-violet screeningagents, colorants and the like which are commonly incorporated byreference. Depending upon the formation technique, the draw ratio andtemperatures, and other conditions, a variety of properties can beimparted to these filaments. The tenacity of the filaments should be atleast 15 grams/denier, preferably at least 20 grams/denier, morepreferably at least 25 grams/denier and most preferably at least 30grams/denier. Similarly, the tensile modulus of the filaments, asmeasured by an Instron tensile testing machine, is at least 300grams/denier, preferably at least 500 grams/denier and more preferablyat least 1,000 grams/denier and most preferably at least 1,200grams/denier. These highest values for tensile modulus and tenacity aregenerally obtainable only by employing solution grown or gel filamentprocesses. Many of the filaments have melting points higher than themelting point of the polymer from which they were formed. Thus, forexample, high molecular weight polyethylene of 150,000, one million andtwo million generally have melting points in the bulk of 138° C. Thehighly oriented polyethylene filaments made of these materials havemelting points of from about 7° to about 13° C. higher. Thus, a slightincrease in melting point reflects the crystalline perfection and highercrystalline orientation of the filaments as compared to the bulkpolymer.

Similarly, highly oriented extended chain polypropylene fibers of weightaverage molecular weight at least 200,000, preferably at least onemillion and more preferably at least two million may be used. Suchextended chain polypropylene may be formed into reasonably well orientedfilaments by the techniques prescribed in the various referencesreferred to above, and especially by the technique of U.S. Pat. No.4,413,110. Since polypropylene is a much less crystalline material thanpolyethylene and contains pendant methyl groups, tenacity valuesachievable with polypropylene are generally substantially lower than thecorresponding values for polyethylene. Accordingly, a suitable tenacityis at least 8 grams/denier, with a preferred tenacity being at least 11grams/denier. The tensile modulus for polypropylene is at least 160grams/denier, preferably at least 200 grams/denier. The melting point ofthe polypropylene is generally raised several degrees by the orientationprocess, such that the polypropylene filament preferably has a mainmelting point of at least 168° C., more preferably at least 170° C. Theparticularly preferred ranges for the above-described parameters canadvantageously provide improved performance in the final article.Employing fibers having a weight average molecular weight of at leastabout 200,000 coupled with the preferred ranges for the above-describedparameters (modulus and tenacity) can provide advantageously improvedperformance in the final article.

High molecular weight polyvinyl alcohol (PV-0H) fibers having hightensile modulus are described in U.S. Pat. No. 4,440,711 to Y. Kwon, etal., which is hereby incorporated by reference to the extent it is notinconsistent herewith. High molecular weight PV-0H fibers should have aweight average molecular weight of at least about 200,000. Particularlyuseful PV-OH fibers should have a modulus of at least about 300g/denier, a tenacity of at least about 7 g/denier (preferably at leastabout 10 g/denier, more preferably at about 14 g/denier and mostpreferably at least about 17 g/denier), and an energy to break of atleast about 8 joules/g. PV-OH fibers having a weight average molecularweight of at least about 200,000, a tenacity of at least about 10g/denier, a modulus of at least about 300 g/denier, and an energy tobreak of about 8 joules/g are more useful in producing a ballisticresistant article. PV-OH fiber having such properties can be produced,for example, by the process disclosed in U.S. Pat. No. 4,599,267.

In the case of polyacrylonitrile (PAN), the PAN fiber should have aweight average molecular weight of at least about 400,000. Particularlyuseful PAN fiber should have a tenacity of at least about 10 g/denierand an energy to break of at least about 8 joule/g. PAN fiber having amolecular weight of at least about 400,000, a tenacity of at least about15 to 20 g/denier and an energy to break of at least about 8 joule/g ismost useful; and such fibers are disclosed, for example, in U.S. Pat.No. 4,535,027.

In the case of aramid fibers, suitable aramid fibers formed principallyfrom aromatic polyamide are described in U.S. Pat. No. 3,671,542, whichis hereby incorporated by reference. Preferred aramid fibers will have atenacity of at least about 20 g/d, a tensile modulus of at least about400 g/d and an energy-to-break at least about 8 joules/gram, andparticularly preferred aramid fibers will have a tenacity of at leastabout 20 g/d, and an energy-to-break of at least about 20 joules/gram.Most preferred aramid fibers will have a tenacity of at least about 20g/denier, a modulus of at least about 900 g/denier and anenergy-to-break of at least about 30 joules/gram. For example,poly(phenylenediamine terephalamide) filaments produced commercially byDupont Corporation under the trade name of Kevlar® 29 and 49 and havingmoderately high moduli and tenacity values are particularly useful informing ballistic resistant composites. (Kevlar® 29 has 500 g/denier and22 g/denier and Kevlar® 49 has 1000 g/denier and 22 g/denier as valuesof modulus and tenacity, respectively). Also useful in the practice ofthis invention is poly(metaphenylene isophthalamide) filaments producedcommercially by Dupont under the trade name Nomex®.

In the case of liquid crystal copolyesters, suitable fibers aredisclosed, for example, in U.S. Pat. Nos. 3,975,487; 4,118,372 and4,161,470.

The high strength fiber network is impregnated with or embedded in amatrix composition by applying the matrix composition to the highstrength fibers and then consolidating the matrix composition/fiberscombination. By "consolidating" is meant that the matrix material andthe fiber network layer are combined into a single unitary layer.Consolidation can occur via drying, cooling, pressure or a combinationthereof. Typically, however, consolidation is achieved substantially, ifnot completely, by drying.

After consolidation, the matrix composition of the invention includes atleast one thermoset vinyl ester and diallyl phthalate. Preferably, thevinyl ester is one produced by the esterification of a polyfunctionalepoxy resin with an unsaturated monocarboxylic acid, usually methacrylicor acrylic acid. Illustrative vinyl esters include diglycidyl adipate,diglycidyl isophthalate, di-(2,3-epoxybutyl) adipate,di-(2,3-epoxybutyl) oxalate, di-(2,3-epoxyhexyl) succinate,di-(3,4-epoxybutyl) maleate, di-(2,3-epoxyoctyl) pimelate,di-(2,3-epoxybutyl) phthalate, di-(2,3-epoxyoctyl) tetrahydrophthalate,di-(4,5-epoxy-dodecyl) maleate, di-(2,3-epoxybutyl) terephthalate,di-(2,3-epoxypentyl) thiodipropronate, di-(5,6-epoxy-tetradecyl)diphenyldicarboxylate, di-(3,4-epoxyheptyl) sulphonyldibutyrate,tri-(2,3-epoxybutyl)-1,2,4-butanetricarboxylate,di-(5,6-epoxypentadecyl)maleate, di-(2,3-epoxybutyl) azelate,di-(3,4-epoxypentadecyl) citrate, di-(4,5-epoxyoctyl)cyclohexane-1,3-dicarboxylate, di-(4,5-epoxyoctadecyl) malonate,bisphenol-A-fumaric acid polyester and similar materials.

The vinyl ester matrix material should have a tenacity of about 10,000to 50,000 psi (6.9×10⁴ to 3.4 ×10⁵ kPa), a tensile modulus of about1×10⁶ to 3×10⁶ psi (6.9×10⁶ to 2.1×10⁷ kPa), a T_(g) (as evidenced by asudden drop in the ductility and elasticity of the material) of lessthan about 165° C., and an elongation-to-break of about 2 to 14%.Particularly preferred are vinyl esters available from Dow Chemical Co.

As mentioned previously, the matrix material typically is applied to thefiber network in the form of a solution. Prior to this invention, if anepoxy-based vinyl ester resin was desired as the matrix material, it wasdiluted with a compound having an unsaturated carbon-carbon double bond(e.g., styrene) and this dilution was mixed with a curing catalyst andadditional solvents. The resulting solution was applied to the fibernetwork and dried to remove the unsaturated carbon-carbon double bondand the additional solvents. The remaining or post-consolidation matrixcomposition consisted of substantially all vinyl ester with only a traceamount of the styrene. Such a system is described in U.S. Pat. No.5,165,989.

The problem with such a system is that the carbon double bondunsaturated organic solvent that was required to be removed have highboiling points. Consequently, the temperature and amount of ovenresidence time required were substantial. For example, a commonconventional unsaturated solvent is styrene, which has a boiling pointof 145° C. In order to volatilize the styrene, the vinylester-impregnated fiber network must be pre-heated and transportedthrough an oven approximately 30 m long at an oven temperature of110°-140°C. According to the present invention, it is not necessary toremove a high boiling point, unsaturated solvent.

It has been found that if a matrix composition system that includesvinyl ester, diallyl phthalate and a low boiling point (boiling pointless than 115° C., preferably less than 90° C.), carbon-carbon saturatedorganic solvent is used, it is not necessary to remove a high boilingpoint, unsaturated solvent. The diallyl phthalate acts as a crosslinkingagent and can remain in the matrix composition after consolidation.

The low boiling point, carbon-carbon saturated organic solvent can be alower (C₁ -C₅) alcohol, a lower ketone (C₃ -C₁₀), a lower (C₁ -C₅)acetate, or a combination thereof. As used herein, "carbon-carbonsaturated" denotes a compound wherein all the bonds between carbon atomsare single bonds. In other words, a carbon-carbon saturated compounddoes not include any unsaturated carbon-carbon double bonds. Preferredsolvents include methyl ethyl ketone, acetone, ethanol, methanol,isopropyl alcohol, cyclohexane, ethyl acetone, and combinations thereof.A catalyst for curing the vinyl ester resin may also be present in thematrix composition applied to the fiber network. Suitable catalysts, byway of example, include tert-butyl perbenzoate,2,5-dimethyl-2,5-di-2-ethylhexanoylperoxyhexane, benzoyl peroxide andcombinations thereof. After consolidation, there is only a trace, ifany, of the low boiling point solvent and catalyst.

Since the matrix composition system of the present invention does notrequire the removal of a high boiling point solvent, the required oventemperature is only about 90°-120° C., preferably 90°-100° C., and theoven length is only about 8 to 14 m. The advantage of the shorter ovenlength is that the alignment of the fiber network does not tend to altersubstantially as it passes through the oven. In ovens reaching up toabout 30 m the dimensional stability of the individual fibers tends todiminish. Consequently, the fibers begin to have random curves and kinksthat compromise the intended fiber alignment.

The matrix composition applied to the fiber network should include about35 to 65, preferably about 45 to 55, weight % vinyl ester, about 2 to 8,preferably about 3 to 6, weight % diallyl phthalate, with the remainderconsisting of low boiling point solvent, based on the total weight ofthe composition. If a curing catalyst is present, it should constituteabout 0.05 to 1.0 weight %, preferably about 0.2 to 0.8 weight %. Afterconsolidation, the matrix composition should include about 5 to 15,preferably about 8 to 12, weight % diallyl phthalate, based on the totalweight of matrix composition, with the remainder consisting essentiallyof vinyl ester.

The matrix composition may be compounded with fillers such as carbonblack, silica, glass microballoons, etc. up to an amount not to exceedabout 300% by weight of the matrix composition, preferably not to exceed100% by weight.

A simple composite can be formed from the matrix-impregnated highstrength fiber networks. "Simple composite" is intended to denote anarticle that includes at least one fiber network combined with a singlemajor matrix material to form a unitary layer, whether or not there areother materials present such as fillers, lubricants or the like. Simplecomposite materials may be constructed and arranged in a variety offorms.

The matrix-impregnated fiber network also can be used to form morecomplex composites. For example, the composite can include a secondmatrix material in addition to the vinyl ester. In a preferredembodiment the second matrix material is in the form of a film which isadjacent to at least one side of the matrix-impregnated fiber network.The matrix-impregnated fiber network can be pressed or embedded into thesecond matrix material so that the second matrix material at leastpartially encompasses the impregnated fibers.

Among second matrix material films which can be used in the inventionare thermoplastic polyolefins, thermoplastic elastomers, crosslinkedthermoplastics, crosslinked elastomers (e.g., ethylene propylene dieneand butyl rubber), polyester, polyamide, fluorocarbon, urethane, epoxy,polyvinylidene chloride, and polyvinyl chloride. Homopolymers orcopolymers of these films preferably are uniaxially or biaxiallyoriented.

It is especially preferred that the film be made of high densitypolyethylene (preferably having a melting point of about 105° C.),polypropylene, or a blend of polyethylene and styrene-isoprene-styreneblock copolymer (available from Raven Industries). Such a film acts asan oxygen barrier, provides surface modification and allows for theseparation of individual layers after they have been manufactured priorto molding of the final article.

In the preferred case of high density polyethylene film, a filmthickness of about 4 to 80 μm, preferably 15 to 25 μm, is used and apressure of about 0.001 to 1.5 kg/mm₂, and a temperature, preferably ofabout 60° to 400° C., more preferably 100° to 160° C., are employed forpressing the impregnated fiber network into the film.

It is convenient to characterize the geometries of such composites bythe geometries of the fibers. One such suitable arrangement is a fibernetwork layer in which the fibers are aligned parallel to one anotheralong a common fiber direction (referred to herein as a"unidirectionally aligned fiber networks"). Successive layers of suchunidirectionally aligned fibers can be rotated with respect to theprevious layer. Preferably, the fiber network layers of the compositeare cross-plied, that is, with the fiber direction of the unidirectionalfibers of each network layer rotated with respect to the fiber directionof the unidirectional fibers of the adjacent layers. An example is afive layer article with the second, third, fourth and fifth layersrotated +45°, -45°, 90° and 0° with respect to the first layer. Apreferred example includes two layers with a 0°/90° layup. Such rotatedunidirectional alignments are described, for example, in U.S. Pat. Nos.4,457,985; 4,748,064; 4,916,000; 4,403,012; 4,623,573; and 4,737,402.

In general, the composite of the invention is formed by applying thematrix composition to the high strength fibers and then consolidatingthe matrix material/fibers combination.

For example, the fiber or yarn can be transported through a solution ofthe matrix composition to substantially coat the fiber or yarn and thendried to form a coated fiber or yarn. The resulting coated fiber or yarncan then be arranged into the desired network configuration to form alayer of ballistic resistant material. Alternatively, the fiber networkcan be constructed initially and then coated with the matrix compositionor embedded into a film of the matrix composition.

The fiber networks can be constructed via a variety of well knownmethods. In the preferred case of unidirectionally aligned fibernetworks yarn bundles of high strength filaments, preferably havingabout 30 to about 2000 individual filaments of less than about 12denier, and more preferably of about 100 individual filaments of lessthan about 7 denier, are supplied from a creel and led through guidesand a spreader bar into a collimating bar prior to coating orimpregnating with the matrix material. The collimating comb aligns thefilaments coplanarly and in a substantially unidirectional fashion.

The fiber network layers typically contain from about 6 to 12 fiber endsper inch (2.4 to 4.7 ends per cm) and preferably 8 to 11 ends per inch(3.2 to 4.3 ends per cm). Each layer (including matrix material) istypically from about 0.01 to 0.2, preferably about 0.04 to 0.12, andmost preferably about 0.06 to 0.10, mil (mm) thick.

In the instances of a simple composite where the matrix composition issupplied in the form of a film, U.S. Pat. No. 5,173,138, herebyincorporated by reference, describes a method for making the matrixmaterial-impregnated fibrous network of the present invention. Thismethod includes feeding a matrix film onto at least one side of thefiber network layer while heating for a time sufficient to impregnatethe fiber network with the film without damaging the fibers and physicalproperties of the resin matrix.

Alternatively, the fiber network layer can be sandwiched between releasepapers, one of which is coated with the wet matrix composition. Thissystem is then passed under a series of pressure rolls to complete theimpregnation of the fibers. The top release paper is pulled off whilethe impregnated network of fibers is subjected to heat to remove thesolvent from the matrix composition.

The preferred method, however, includes initially forming the fibernetwork layer, preferably a unidirectional network as described above,applying a solution of the matrix composition onto the fiber networklayer, and then drying the matrix-impregnated fiber network layer asdescribed, for example, in U.S. Pat. No. 4,820,568, incorporated hereinby reference. As shown in FIG. 1, yarn is supplied from a creel 102 andpassed through a combing station 104 to form the fiber network. Thefiber network then is placed on a carrier web which can be a paper or afilm substrate 106. The matrix composition is applied to the fibernetwork layer by coating a solution of the matrix composition onto thefiber network layer at 108. The coated fiber network then is passedthrough a pair of rollers 110. The rollers spread the matrix compositionsubstantially uniformly among the fibers. The impregnated fiber networklayer is then passed through a heated oven 112 for drying. Nip roller114 is used to control final layer thickness. Nip roller 116 is used topull the carrier web and prepreg through the system. The substrate andthe impregnated fiber network layer can then be wound on roller 118. Inthe oven, the impregnated fiber network layer is subjected to sufficientheat to volatilize the solvent for the matrix composition.

If the second matrix material is desired, a preferred method for makingthe fiber network layer employs a separate film of a second matrixmaterial upon which the high strength fiber or yarn is disposed and thencoated. More specifically, the high strength fibers are transportedthrough a comb means which collimates the fibers to form aunidirectionally aligned fiber network. The unidirectional fibers arelaid onto a moving film of the second matrix material. A solution of thevinyl ester-containing matrix composition then is coated onto the fiberswhich are laying on the film, thereby adhering the fibers to the film.The vinyl ester-containing matrix composition may penetrate between thefibers and the film and should occupy substantially all the void spacebetween the fibers, although some void spaces may remain. The vinylester-containing matrix composition is subsequently dried. The coatingand drying steps can be repeated to achieve the desired amounts ofmatrix material relative to the amount of fiber. An apparatus forcarrying out this method is described in U.S. Pat. No. 5,149,391, herebyincorporated by reference.

The proportion of matrix composition to fiber in the composite may varywidely, depending upon the end use. If the density of the matrixcomposition is similar to that of the fiber, then the matrix compositionmay generally form from about 10 to about 40% by weight, preferablyabout 14 to 30%, more preferably 16 to 28%, and most preferably about 20to 24%, based on the weight of an individual layer or the finalcomposite. For ballistic resistant composite articles, the preferredrange is up to 28% by weight. If the densities of the matrix compositionand fiber are dissimilar, then the matrix composition may form fromabout 5 to about 40% by volume, preferably about 6 to 30%, morepreferably 7 to 24%, and most preferably about 8 to 22%, based on thevolume of an individual layer or the final composite. In the embodimentswhich include a second matrix material, then the vinyl ester matrixmaterial may generally form from about 5 to about 35% by weight,preferably about 10 to 28%, and most preferably about 20 to 24%, and thesecond matrix material may correspondingly generally form from about 5to about 30% by weight, preferably about 6 to 14% by weight, morepreferably 7 to 14%, and most preferably about 8 to 12%, based on theweight of the layer or the final composite.

The individual consolidated fiber network layers can be laid up into astack for formation into the end use composite or they can be formedinto a prepreg element which is subsequently used to form the end usecomposite. By "end use composite" is meant the integral multi-layercomposite which is used in an article such as a helmet or vehicle armorplates. As mentioned previously, the most preferred composite is onewherein the fiber network of each layer is unidirectionally aligned andoriented so that the fiber directions in adjacent layers are in a 0°/90°configuration.

In the most preferred embodiment, two fiber network layers arecross-plied in the 0°/90° configuration and then molded to form aprepreg element. The two fiber network layers can be continuouslycross-plied, preferably by cutting one of the networks into lengths thatcan be placed successively across the width of the other network in a0°/90° orientation. U.S. Pat. No. 5,173,138 describes an apparatus forcontinuous cross-plying. As described in PCT Publication No. WO91/12136, the resulting continuous ply can then be wound into a rollwith a layer of separation material between each ply. The roll is thensubjected to pressure and/or heat in order to adhere the two cross-pliedfiber networks together.

The temperatures and/or pressures to which the fiber network layers areexposed for molding vary depending upon the type of high strength fiberused. The end use composite for use in armor panels can be made bymolding a stack of fiber network layers or prepreg elements under apressure of about 150 to 400, preferably about 180 to 250, psi and atemperature of about 220° to 260° F. The end use composite for use inhelmets can be made by molding a stack of fiber network layers orprepreg elements under a pressure of about 1500 to 3000, preferablyabout 1800 to 2200, psi and a temperature of about 220° to 260° F.

The following examples are presented to demonstrate the advantages ofthe invention. The specific techniques, conditions, materials,proportions and reported data set forth to illustrate the principles ofthe invention are exemplary and should not be construed as limiting thescope of the invention.

The total areal density (ADT) indicates the weight of fiber and matrixmaterial per unit area of an individual fiber network layer.

Fragment ballistic testing of the examples was performed in accordancewith Military Specification MIL-P-662E using a 17 grain fragmentsimulation projectile (FSP) in accordance with the specifications ofMilitary Specification MIL-P-46593A. The protective power of the sampleis expressed by citing the impacting velocity at which 50% of theprojectiles are stopped which is designated the V₅₀ value.

EXAMPLE 1

A unidirectionally aligned network of 1300 denier extended chainpolyethylene yarn available from AlliedSignal under the tradenameSpectra® 1000 was coated with 5000 g of a solution mixture availablefrom Dow Chemical Co. that consisted of 63 weight % vinyl ester, 31weight % methyl ethyl ketone and 6 weight % diallyl phthalate. Thissolution mixture was combined with 35 g of2,5-dimethyl-2,5-di-2-ethylhexanoylperoxyhexane (commercially availablefrom Atochem North America under the tradename Lupersol 256) and 1900 gof methyl ethyl ketone available from Industrial Chemical. The vinylester has a reported tenacity of 20,700 psi, a tensile modulus of1.74×10⁶ psi, and an elongation-to-break of 5-6%. The coated network wasthen passed through an oven to volatilize and remove the methyl ethylketone. The dried fiber network layer had 20% by weight of matrixcomposition and 78% by weight fiber. Two of these network layers werestacked in a 0°/90° fiber alignment and molded four times for a periodof 5 minutes at a temperature of 150° F. and a pressure of 100 psi toform a prepreg element. Thirteen layers of these prepreg elements werestacked and molded at a temperature of 240° F. and a pressure of 400 psifor a period of 10 minutes in order to make a panel. The areal densityof the panel was 1.45 lb/ft². The panel was tested as described aboveagainst a FSP and found to have a V₅₀ of 2148 ft/sec.

EXAMPLE 2

Another panel was made as described in Example 1 and it had an arealdensity of 1.37 lb/ft². The V₅₀ against an FSP was 2050 ft/sec.

EXAMPLE 3

Using 13 layers of prepreg elements made as described in Example 1, amilitary-type helmet was molded in a matched-die steel mold. The surfacearea of the helmet was 1.29 ft². The outside and inside of the helmetconsisted of a fabric layer of woven 1200 denier extended chainpolyethylene yarn available from AlliedSignal under the tradenameSpectra® fabric style 903 that had been coated with a vinyl ester resinavailable from Dow Chemical Co. under the tradename DERAKANE 411-45. Theweight of the helmet shell was 2.14 lbs. Forty-eight hours aftermolding, the helmet was tested against a FSP as described above and wasfound to have a V₅₀ of 2317 ft/sec.

EXAMPLE 4

Another military-type helmet was made according to the proceduredescribed in Example 3. The weight of the helmet shell was 2.22 lbs andthe resistance against FSP fragment was 2280 ft/sec.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

We claim:
 1. A method for producing a ballistic resistant article thatincludes at least one network of high strength fibers in a matrixcomposition, wherein the high strength fibers have a tenacity of atleast about 7 g/d, a tensile modulus of at least about 150 g/d and anenergy-to-break of at least about 8 J/g, the method comprising applyinga mixture consisting essentially of at least one thermoset vinyl ester,an optional catalyst for curing the thermoset vinyl ester, diallylphthalate and at least one carbon-carbon saturated solvent having aboiling point lower than about 115° C. to a high strength fiber networkfollowed by consolidating the coated high strength fiber network at atemperature higher than the boiling point of the solvent and lower thanabout 120° C. to substantially remove the carbon-carbon saturatedsolvent.
 2. A method according to claim 1, wherein the carbon-carbonsaturated solvent is selected from the group consisting of an alcoholthat contains 1 to 5 carbon atoms, a ketone that contains 3 to 10 carbonatoms and an acetate that contains 1 to 5 carbon atoms.
 3. A methodaccording to claim 1 wherein the carbon-carbon saturated solvent isselected from the group consisting of methyl ethyl ketone, acetone,ethanol, methanol, isopropyl alcohol, cyclohexane and ethyl acetone. 4.A method according to claim 3, wherein the carbon-carbon saturatedsolvent is methyl ethyl ketone.
 5. A method according to claim 1,wherein the curing catalyst is selected from the group consisting oftert-butyl perbenzoate, 2,5-dimethyl-2,5-di-2-ethylhexanoylperoxyhexaneand benzoyl peroxide.
 6. A method for producing a ballistic resistantarticle that includes at least one network of high strength fibers in amatrix composition, wherein the high strength fibers have a tenacity ofat least about 7 g/d, a tensile modulus of at least about 150 g/d and anenergy-to-break of at least about 8 J/g, the method comprising coating ahigh strength fiber network with a solution consisting essentially of atleast one thermoset vinyl ester, an optional catalyst for curing thethermoset vinyl ester, diallyl phthalate and at least one carbon-carbonsaturated solvent having a boiling point lower than about 115° C.followed by drying the coated high strength fiber network at atemperature higher than the boiling point of the solvent and lower thanabout 120° C. to substantially remove the carbon-carbon saturatedsolvent.
 7. A method according to claim 6 wherein the carbon-carbonsaturated solvent is methyl ethyl ketone and the drying step is effectedby transporting the coated high strength fiber network through an ovenhaving a length of about 8 to 14 m at a temperature of about 90° to 120°C.
 8. A method according to claim 1 wherein the solvent has a boilingpoint of less than about 90° C.
 9. A method according to claim 1 whereinthe consolidating step occurs at a temperature of about 90° to 120° C.10. A method according to claim 1 wherein the consolidating step occursat a temperature of about 90° to 100° C.
 11. A method according to claim6 wherein the solvent has a boiling point of less than about 90° C. 12.A method according to claim 6 wherein the drying step occurs at atemperature of about 90° to 120° C.
 13. A method according to claim 12wherein the drying step occurs at a temperature of about 90° to 100° C.14. A ballistic resistant article made in accordance with the method ofclaim
 1. 15. A ballistic resistant article made in accordance with themethod of claim 6.